Chemistry: Universal Indicator and Salts

Study Notes

Universal indicator consists of a mixture of dyes that display a spectrum of colors based on acidity or alkalinity of a solution.
Different colors are produced at varying concentrations of hydrogen ions.
Salts are compounds formed by the replacement of hydrogen atoms of an acid with metallic or ammonium ions.

Normal Salts: Formed by complete replacement of hydrogen ions; e.g., hydrochloric acid yields sodium chloride.
Acid Salts: Result from partial replacement of hydrogen ions from polybasic acids; e.g., dibasic sulphuric acid yields sodium hydrogen sulphate (NaHSO4).
Basic Salts: Derived from partial replacement of hydroxyl groups of bases with acid radicals; e.g., basic lead chloride [Pb(OH)Cl].

By Source:
- Organic Acids: Obtained from plants (e.g., acetic acid, citric acid); weak acids.
- Inorganic Acids: Obtainable from minerals (e.g., hydrochloric acid); strong acids due to complete ionization.
By Concentration:
- Concentrated Acid: Higher acid content than water.
- Dilute Acid: Higher water content than acid.
By Basicity:
- Monobasic Acid: Produces one hydronium ion (e.g., HCl).
- Dibasic Acid: Produces two hydronium ions (e.g., sulphuric acid).
- Tribasic Acid: Produces three hydronium ions (e.g., phosphoric acid).

Sour taste and various physical states (solids like boric acid, liquid like HCl).
Corrosive to skin (e.g., sulfuric acid is black, hydrochloric acid is amber).
Change indicator colors (blue litmus to red, methyl orange to pink, phenolphthalein remains unchanged).
Olfactory Indicators: Substances with scent changes in acidic/basic environments (e.g., onion, vanilla, clove oil).

React with active metals to form hydrogen and metal salts.
Neutralization reaction with bases.
React with carbonates to form salt, water, and carbon dioxide.
Form salt, water, and sulfur dioxide when reacting with sulfites and bisulfites.
React with sulfides to yield salt and hydrogen sulfide.
Limited reactions with some chlorides and nitrates.

Bases include metallic oxides, metallic hydroxides, or ammonium hydroxide; they react with hydronium ions to form salt and water.

By Strength:
- Strong Base: Completely ionizes in solution.
- Weak Base: Partially ionizes in solution.
By Acidity:
- Monoacidic Base: Produces one OH- ion.
- Diacidic Base: Produces two OH- ions.
- Triacidic Base: Produces three OH- ions.

Physical properties include a bitter taste, slippery feel, and ability to change indicator colors (e.g., red litmus to blue).
Strong electrolytes that can absorb carbon dioxide to form carbonates.
Neutralize acids producing salt and water.
Precipitate insoluble hydroxides with heavy metal salts (e.g., copper, iron, zinc).
Release ammonia gas when warmed with ammonium salts.